Multi-piece solid golf ball

ABSTRACT

A multi-piece solid golf ball has a solid core obtained by molding and vulcanizing a rubber composition which includes (A) a base rubber containing a polybutadiene synthesized using a rare-earth catalyst, (B) an unsaturated carboxylic acid and/or a metal salt thereof, (C) an organic sulfur compound, (D) an inorganic filler and (E) an organic peroxide. The core is enclosed within a mantle of one or more layer which is made primarily of a thermoplastic resin and has a Durometer D hardness of 30 to 70. The mantle is enclosed within a cover which is made primarily of a thermoplastic polyurethane and which has a Durometer D hardness of 40 to 60 that is lower than the Durometer D hardness of the outermost layer of the mantle. This construction provides the golf ball with an outstanding rebound.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to multi-piece solid gold balls such asfour-piece solid golf balls.

2. Prior Art

The polybutadiene formulations used as the base rubber in golf ballshave hitherto been modified and improved in various ways to confer thegolf balls with outstanding rebound characteristics.

For example, JP-A 62-89750 discloses rubber compositions for solid golfballs which are obtained by formulating as the base rubber apolybutadiene having a Mooney viscosity of 70 to 100 and synthesizedusing a nickel or cobalt catalyst, in combination with either apolybutadiene having a Mooney viscosity of 30 to 90 and synthesizedusing a lanthanide series catalyst or a polybutadiene having a Mooneyviscosity of 20 to 50 and synthesized using a nickel or cobalt catalyst.However, further improvement is desired in the rebound characteristicsafforded by these rubber compositions.

JP-A 2-268778 describes golf balls obtained by compounding apolybutadiene having a Mooney viscosity of less than 50 and synthesizedusing a group VIII catalyst with a polybutadiene having a Mooneyviscosity of less than 50 and synthesized using a lanthanide catalyst.Unfortunately, such golf balls have poor rebound characteristics.

In addition, JP-A 11-70187 discloses multi-piece solid golf balls inwhich the mantle is made of a polybutadiene having a low Mooneyviscosity. JP-A 11-319148 teaches solid golf balls obtained using arubber composition formulated from a polybutadiene having a Mooneyviscosity of 50 to 69 and synthesized using a nickel or cobalt catalystin combination with a polybutadiene having a Mooney viscosity of 20 to90 and synthesized using a lanthanide series catalyst. JP-A 11-164912describes solid golf balls obtained using a rubber composition having a1,2-vinyl unit content of not more than 2.0% and having a ratio Mw/Mn ofthe weight-average molecular weight to the number-average molecularweight of not more than 3.5. JP-A 63-275356 discloses golf balls madewith a rubber composition formulated using a high Mooney viscositypolybutadiene. JP-A 3-151985 describes golf balls made with a rubbercomposition formulated using a polybutadiene having a highnumber-average molecular weight in combination with a polybutadienehaving a low number-average molecular weight. However, the golf balls inall of these prior-art disclosures have inadequate reboundcharacteristics.

Also, JP-A 61-71070 mentions the use of two types of organic peroxidesand JP-A 62-112574 mentions the use of a small amount of organicperoxide. Yet, the golf balls obtained in both of these disclosures haveinadequate rebound characteristics. Moreover, crosslinking takes a longtime, considerably diminishing productivity during manufacture of thegolf balls.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide golf ballswhich have a high rebound and exert a good flight performance.

We have found that golf balls of excellent manufacturability and goodrebound characteristics can be obtained when the solid core of the ballis made of a molded and vulcanized rubber composition containing a baserubber composed primarily of a polybutadiene of at least 60 wt % cis-1,4structure and synthesized using a rare-earth catalyst, and containingalso 0.1 to 0.8 parts by weight of an organic peroxide per 100 parts byweight of the base rubber. That is, in the prior art, lowering theamount of organic peroxide has increased the vulcanization time, leadingto a decline in productivity and has also resulted in poor reboundcharacteristics. However, we have discovered that by usinghigh-resilience polybutadiene synthesized with a rare-earth catalyst andby including in the rubber composition 0.1 to 0.8 part by weight ofpreferably two or more types of organic peroxides with significantlydiffering half-lives, the ease of operation is improved, thevulcanization time is shortened and even productivity can be enhanced,in addition to which further improvements in the rebound characteristicsof the golf ball can also be achieved.

Such an increase in rebound allows the core and the ball as a whole tobe made correspondingly softer, resulting in desirable initialconditions (i.e., low spin and high angle of elevation) and increasedcarry on a full shot with a driver. Moreover, a soft feel on impact canalso be achieved.

Accordingly, in a first aspect, the invention provides a multi-piecesolid golf ball constructed of a solid core, a mantle of at least onelayer and a cover. The core is obtained by molding and vulcanizing arubber composition comprising (A) 100 parts by weight of a base rubberwhich includes 60 to 100 wt % of a polybutadiene of at least 60 wt %cis-1,4 structure and synthesized using a rare-earth catalyst, (B) anunsaturated carboxylic acid and/or an unsaturated carboxylic acid metalsalt, (C) an organic sulfur compound, (D) an inorganic filler and (E)0.1 to 0.8 part by weight of organic peroxide, has a diameter of 30 to40 mm and has a deflection when subjected to a load of 980 N (100 kg) of2.5 to 6.0 mm. The mantle is made primarily of a thermoplastic resin,has a thickness of at least 0.5 mm, has a Durometer D hardness of 30 to70, and includes an outermost layer which is in contact with the coverand has a specific Durometer D hardness. The cover is made primarily ofa thermoplastic polyurethane, has a thickness of 0.5 to 2.5 mm and has aDurometer D hardness of 40 to 60 which is lower than the Durometer Dhardness of the outermost layer of the mantle. The golf ball has adeflection when subjected to a load of 980 N (100 kg) of 2.0 to 4.0 mm.This golf ball exhibits an excellent spin performance and excellentflight characteristics.

To provide the golf ball with an even better spin performance and betterflight characteristics, the outermost layer of the mantle in contactwith the cover has a Durometer D hardness of preferably 45 to 70.

To further enhance the rebound characteristics of the ball, thepolybutadiene in the base rubber of the rubber composition is preferablya modified polybutadiene rubber synthesized using a neodymium catalyst,followed by reaction with a terminal modifier.

The rubber composition from which the core is made preferably includes(A) 100 parts by weight of a base rubber, (B) 10 to 60 parts by weightof an unsaturated carboxylic acid and/or an unsaturated carboxylic acidmetal salt, (C) 0.1 to 5 parts by weight of an organic sulfur compound,(D) 5 to 80 parts by weight of an inorganic filler, and (E) 0.1 to 0.8part by weight of at least two different organic peroxides. This rubbercomposition can further enhance the rebound characteristics of the golfball, and can also optimize the hardness and weight of the ball.

The cover is preferably made of a composition consisting essentially of(G) a thermoplastic polyurethane material, and (H) an isocyanate mixtureobtained by dispersing (h1) an isocyanate compound bearing as functionalgroups at least two isocyanate groups per molecule in (h2) athermoplastic resin which substantially does not react with isocyanate.A cover of this composition can provide the ball with improved scuffresistance.

In one preferred embodiment, at least one layer of the mantle in thegolf ball according to the first aspect of the invention is made of amixture composed of 100 parts by weight of resin components whichinclude a base resin of (M) an olefin/unsaturated carboxylic acid binaryrandom copolymer and/or a metal ion neutralization product of anolefin/unsaturated carboxylic acid binary random copolymer, and (N) anolefin/unsaturated carboxylic acid/unsaturated carboxylic acid esterternary random copolymer and/or a metal ion neutralization product of anolefin/unsaturated carboxylic acid/unsaturated carboxylic acid esterternary random copolymer in a weight ratio M/N of 100:0 to 25:75, incombination with (P) a non-ionomeric thermoplastic elastomer in a weightratio (M+N)/P of 100:0 to 50:50; (O) 5 to 80 parts by weight of a fattyacid and/or fatty acid derivative having a molecular weight of 280 to1,500; and (R) 0.1 to 10 parts by weight of a basic inorganic metalcompound capable of neutralizing un-neutralized acid groups in the baseresin and component Q. A mantle layer of this composition furtherenhances the rebound characteristics of the ball.

In another preferred embodiment, at least one layer of the mantle in thegolf ball according to the first aspect of the invention is made of amixture composed of resin components which include at least one baseresin selected from the group consisting of (M) olefin/unsaturatedcarboxylic acid binary random copolymers and metal ion neutralizationproducts thereof and (N) olefin/unsaturated carboxylic acid/unsaturatedcarboxylic acid ester ternary random copolymers and metal ionneutralization products thereof, in combination with (P) a non-ionomericthermoplastic elastomer in a weight ratio (M+N)/P of 100:0 to 50:50; (O)a fatty acid and/or fatty acid derivative having a molecular weight of280 to 1,500; (R) a metal ion source capable of neutralizingun-neutralized acid groups in the base resin and component Q; and (S) acompound having a molecular weight of not more than 20,000 which bearsat least two reactive functional groups. A mantle constituted in thisway improves adhesion between the cover and the underlying layer, andenhances both the rebound characteristics and the durability of theball.

To achieve both good ball softness and good rebound characteristics, itis preferable for at least one layer of the mantle to be made primarilyof a thermoplastic polyester.

In a second aspect, the invention provides a four-piece solid golf ballconstructed of a solid core, a two-layer mantle and a cover. The core isobtained by molding and vulcanizing a rubber composition comprising (A)100 parts by weight of a base rubber which includes 60 to 100 wt % of apolybutadiene of at least 60% cis-1,4 structure and synthesized using arare-earth catalyst, (B) an unsaturated carboxylic acid and/or anunsaturated carboxylic acid metal salt, (C) an organic sulfur compound,(D) an inorganic filler and (E) 0.1 to 0.8 part by weight of organicperoxide, has a diameter of 30 to 40 mm and has a deflection whensubjected to a load of 980 N (100 kg) of 2.5 to 6.0 mm. The mantle iscomposed of an inner layer and an outer layer which is in contact withthe cover, each of the two layers being made of a thermoplastic resin,having a thickness of 0.5 to 2 mm and having a Durometer D hardness of30 to 70. The cover is made primarily of a thermoplastic polyurethane,has a thickness of 0.5 to 2.5 mm and has a Durometer D hardness of 40 to60 which is lower than the Durometer D hardness of the outer layer ofthe mantle. The golf ball has a deflection when subjected to a load of980 N (100 kg) of 2.0 to 4.0 mm. This golf ball exhibits an excellentspin performance and excellent flight characteristics.

To provide the four-piece solid golf ball according to the second aspectof the invention with an even better spin performance and better flightcharacteristics, the outer layer of the mantle in contact with the coverhas a Durometer D hardness of preferably 45 to 70.

To further enhance the rebound characteristics of the golf ballaccording to the second aspect of the invention, the polybutadiene inthe base rubber of the rubber composition is typically a modifiedpolybutadiene rubber synthesized using a neodymium catalyst, followed byreaction with a terminal modifier.

The rubber composition from which the core in such a golf ball is madepreferably includes (A) 100 parts by weight of a base rubber, (B) 10 to60 parts by weight of an unsaturated carboxylic acid and/or anunsaturated carboxylic acid metal salt, (C) 0.1 to 5 parts by weight ofan organic sulfur compound, (D) 5 to 80 parts by weight of an inorganicfiller, and (E) 0.1 to 0.8 part by weight of at least two differentorganic peroxides. This rubber composition can further enhance therebound characteristics of the golf ball and can also optimize thehardness and weight of the ball.

The cover in the golf ball according to the second aspect of theinvention is preferably made of a composition consisting essentially of(G) a thermoplastic polyurethane material, and (H) an isocyanate mixtureobtained by dispersing (h1) an isocyanate compound bearing as functionalgroups at least two isocyanate groups per molecule in (h2) athermoplastic resin which substantially does not react with isocyanate.A cover of this composition can provide the ball with improved scuffresistance.

In one preferred embodiment of the golf ball according to the secondaspect of the invention, at least one layer of the mantle is made of amixture composed of 100 parts by weight of resin components whichinclude a base resin of (M) an olefin/unsaturated carboxylic acid binaryrandom copolymer and/or a metal ion neutralization product of anolefin/unsaturated carboxylic acid binary random copolymer, and (N) anolefin/unsaturated carboxylic acid/unsaturated carboxylic acid esterternary random copolymer and/or a metal ion neutralization product of anolefin/unsaturated carboxylic acid/unsaturated carboxylic acid esterternary random copolymer in a weight ratio M/N of 100:0 to 25:75, incombination with (P) a non-ionomeric thermoplastic elastomer in a weightratio (M+N)/P of 100:0 to 50:50; (O) 5 to 80 parts by weight of a fattyacid and/or fatty acid derivative having a molecular weight of 280 to1,500; and (R) 0.1 to 10 parts by weight of a basic inorganic metalcompound capable of neutralizing un-neutralized acid groups in the baseresin and component Q. A mantle layer of this composition furtherenhances the rebound characteristics of the ball.

In another preferred embodiment of the golf ball according to the secondaspect of the invention, at least one layer of the mantle is made of amixture composed of resin components which include at least one baseresin selected from the group consisting of (M) olefin/unsaturatedcarboxylic acid binary random copolymers and metal ion neutralizationproducts thereof and (N) olefin/unsaturated carboxylic acid/unsaturatedcarboxylic acid ester ternary random copolymers and metal ionneutralization products thereof, in combination with (P) a non-ionomericthermoplastic elastomer in a weight ratio (M+N)/P of 100:0 to 50:50; (O)a fatty acid and/or fatty acid derivative having a molecular weight of280 to 1,500; (R) a metal ion source capable of neutralizingun-neutralized acid groups in the base resin and component Q; and (S) acompound having a molecular weight of not more than 20,000 which bearsat least two reactive functional groups. A mantle constituted in thisway improves adhesion between the cover and the underlying layer, andenhances both the rebound characteristics and the durability of theball.

To achieve both good ball softness and good rebound characteristics, itis preferable for the outer layer or the inner layer of the mantle inthe golf ball according to the second aspect of the invention to be madeprimarily of a thermoplastic polyester.

DETAILED DESCRIPTION OF THE INVENTION

The golf balls according to the invention have a core obtained bymolding and vulcanizing a rubber composition containing (A) a baserubber which includes primarily a polybutadiene of at least 60 wt %cis-1,4 structure, has a Mooney viscosity (ML₁₊₄ (100° C.)) ofpreferably at least 40 and is synthesized using a rare-earth catalyst,(B) an unsaturated carboxylic acid and/or an unsaturated carboxylic acidmetal salt, (C) an organic sulfur compound, (D) an inorganic filler and(E) an organic peroxide.

The polybutadiene in component A has a cis-1,4 unit content of at least60 wt %, preferably at least 80 wt %, more preferably at least 90 wt %,and most preferably at least 95 wt %. A polybutadiene having too low acis-1,4 unit content will lower the resilience of the core.

It is desirable for the polybutadiene to have a Mooney viscosity (ML₁₊₄(100° C.)) of at least 40, preferably at least 50, more preferably atleast 52, and most preferably at least 54, but not more than 140,preferably not more than 120, more preferably not more than 100, andmost preferably not more than 80.

The term “Mooney viscosity” used herein refers to an industrial index ofviscosity (see JIS K6300) as measured with a Mooney viscometer, which isa type of rotary plastometer. This value is represented by the symbolML₁₊₄ (100° C.), wherein “M” stands for Mooney viscosity, “L” stands forlarge rotor (L-type), and “1+4” stands for a pre-heating time of 1minute and a rotor rotation time of 4 minutes. The “100“C” indicatesthat measurement was carried out at a temperature of 100° C.

The polybutadiene employed in the invention must be one synthesizedusing a rare-earth catalyst. A known rare-earth catalyst may be used forthis purpose.

Exemplary catalysts include lanthanide series rare-earth compounds incombination with organoaluminum compounds, alumoxanes, halogen-bearingcompounds or Lewis bases.

Examples of suitable lanthanide series rare-earth compounds includehalides, carboxylates, alcoholates, thioalcoholates and amides of atomicnumber 57 to 71 metals.

Organoaluminum compounds that may be used include those of the formulaAlR¹R²R³ (wherein R¹, R² and R³ are each independently a hydrogen or ahydrocarbon residue of 1 to 8 carbons).

Preferred alumoxanes include compounds of the structures shown informulas (I) and (II) below. The alumoxane association complexesdescribed in Fine Chemical 23, No. 9, 5 (1994), J. Am. Chem. Soc. 115,4971 (1993), and J. Am. Chem. Soc. 117, 6465 (1995) are also acceptable.

In the above formulas, R⁴ is a hydrocarbon group having 1 to 20 carbonatoms, and n is 2 or a larger integer.

Examples of halogen-bearing compounds that may be used include aluminumhalides of the formula AlX_(n)R_(3-n) (wherein X is a halogen; R is ahydrocarbon residue of 1 to 20 carbons, such as an alkyl, aryl oraralkyl; and n is 1, 1.5, 2 or 3); strontium halides such as Me₃SrCl,Me₂SrCl₂, MeSrHCl₂ and MeSrCl₃ (wherein “Me” stands for methyl); andother metal halides such as silicon tetrachloride, tin tetrachloride andtitanium tetrachloride.

The Lewis base can be used to form a complex with the lanthanide seriesrare-earth compound. Illustrative examples include acetylacetone andketone alcohols.

In the practice of the invention, the use of a neodymium catalyst inwhich a neodymium compound serves as the lanthanide series rare-earthcompound is advantageous because it enables a polybutadiene rubberhaving a high cis-1,4 unit content and a low 1,2-vinyl unit content tobe obtained at an excellent polymerization activity. Preferred examplesof such rare-earth catalysts include those mentioned in JP-A 11-35633.

To achieve a polybutadiene having a cis unit content within the aboverange and a polydispersity index Mw/Mn within the subsequently describedrange, the polymerization of butadiene in the presence of a rare-earthcatalyst containing a lanthanide series rare-earth compound is carriedout at a butadiene/(lanthanide series rare-earth compound) molar ratioof preferably 1,000 to 2,000,000, and especially 5,000 to 1,000,000, andat an AlR¹R²R³/(lanthanide series rare-earth compound) molar ratio of 1to 1,000, and especially 3 to 500. It is also preferable for the(halogen compound)/(lanthanide series rare-earth compound) molar ratioto be 0.1 to 30, and especially 0.2 to 15, and for the (Lewisbase)/(lanthanide series rare-earth compound) molar ratio to be 0 to 30,and especially 1 to 10.

The polymerization of butadiene in the presence of a rare-earth catalystmay be carried out in a solvent or by bulk polymerization or vapor phasepolymerization, without the use of solvent, and at a polymerizationtemperature in a range of generally −30° C. to +150° C., and preferably10° C. to 100° C.

According to a preferred embodiment of the invention, the polybutadienein component A may be a modified polybutadiene obtained bypolymerization using the above-described rare-earth catalyst, followedby the reaction of a terminal modifier with active end groups on thepolymer.

The modified polybutadiene rubber can be prepared by polymerization asdescribed above, followed by the use of a terminal modifier selectedfrom among types (1) to (7) below. (1) The modified polybutadiene rubbercan be obtained by reacting an alkoxysilyl group-bearing compound withactive end groups on the polymer. Preferred alkoxysilyl group-bearingcompounds are alkoxysilane compounds having at least one epoxy group orisocyanate group on the molecule. Specific examples include epoxygroup-bearing alkoxysilanes such as 3-glycidyloxypropyltrimethoxysilane,3-glycidyloxypropyltriethoxysilane,(3-glycidyloxypropyl)methyldimethoxysilane,(3-glycidyloxypropyl)methyldiethoxysilane,β-(3,4-epoxycyclohexyl)trimethoxysilane,β-(3,4-epoxycyclohexyl)triethoxysilane,β-(3,4-epoxycyclohexyl)methyldimethoxysilane,β-(3,4-epoxycyclohexyl)ethyldimethoxysilane, condensation products of3-glycidyloxypropyltrimethoxysilane and condensation products of(3-glycidyloxypropyl)methyldimethoxysilane; and isocyanate group-bearingalkoxysilane compounds such as 3-isocyanatopropyltrimethoxysilane,3-isocyanatopropyltriethoxysilane,(3-isocyanatopropyl)methyldimethoxysilane,(3-isocyanatopropyl)methyldiethoxysilane, condensation products of3-isocyanatopropyltrimethoxysilane and condensation products of(3-isocyanatopropyl)methyldimethoxysilane.

A Lewis acid can be added to accelerate the reaction when the abovealkoxysilyl group-bearing compound is reacted with active end groups.The Lewis acid acts as a catalyst to promote the coupling reaction, thusimproving cold flow by the modified polymer and providing a better shelfstability. Examples of suitable Lewis acids include dialkyltin dialkylmalates, dialkyltin dicarboxylates and aluminum trialkoxides.

Other types of terminal modifiers that may be used include:

-   (2) halogenated organometallic compounds, halogenated metallic    compounds and organometallic compounds of the general formulas R_(n)    ⁵M′X_(4-n), M′X₄, M′ X₃, R_(n) ⁵M′ (—R⁶—COOR⁷)_(4-n) or R_(n) ⁵M′    (—R⁶—COR⁷)_(4-n) (wherein R⁵ and R⁶ are each independently a    hydrocarbon group of 1 to 20 carbons; R⁷ is a hydrocarbon group of 1    to 20 carbons which may contain pendant carbonyl or ester groups; M′    is a tin, silicon, germanium or phosphorus atom; X is a halogen    atom; and n is an integer from 0 to 3);-   (3) heterocumulene compounds having on the molecule a Y═C═Z linkage    (wherein Y is a carbon, oxygen, nitrogen or sulfur atom; and Z is an    oxygen, nitrogen or sulfur atom);-   (4) three-membered heterocyclic compounds containing on the molecule    the following bonds-    (wherein Y is an oxygen, nitrogen or sulfur atom);-   (5) halogenated isocyano compounds;-   (6) carboxylic acids, acid halides, ester compounds, carbonate    compounds and acid anhydrides of the formula R⁸—(COOH)_(m),    R⁹(COX)_(m), R¹⁰—(COO—R¹¹)_(m), R¹²—OCOO—R¹³ and    R¹⁴—(COOCO—R¹⁵)_(m), and compounds of the formula:-    (wherein R⁸ to R¹⁶ are each independently a hydrocarbon group of 1    to 50 carbons, X is a halogen atom, and m is an integer from 1 to    5); and-   (7) carboxylic acid metal salts of the formula R₁ ¹⁷M″(OCOR¹⁸)₄₋₁,    R₁ ¹⁹M″(OCO—R²⁰—COOR²¹)₄₋₁ or-    (wherein R¹⁷ to R²³ are each independently a hydrocarbon group of 1    to 20 carbons, M” is a tin, silicon or germanium atom, and 1 is an    integer from 0 to 3).

The above terminal modifiers and methods for their reaction aredescribed in, for example, JP-A 11-35633, JP-A 7-268132 and JP-A2002-293996.

It is advantageous for the polybutadiene used in the invention to have apolydispersity index Mw/Mn (where Mw is the weight-average molecularweight and Mn is the number-average molecular weight) of at least 2.0,preferably at least 2.2, more preferably at least 2.4, and mostpreferably at least 2.6, but not more than 8.0, preferably not more than7.5, more preferably not more than 4.0, and most preferably not morethan 3.4. If the polydispersity index Mw/Mn is too low, the rubbercomposition may be more difficult to work. On the other hand, if Mw/Mnis too large, the solid core obtained therefrom may have a lowerresilience.

The invention uses a base rubber composed primarily of theabove-described polybutadiene. The polybutadiene content within the baserubber is at least 60 wt %, preferably at least 70 wt %, more preferablyat least 80 wt %, and most preferably at least 85 wt %. The content ofthe above polybutadiene in the base rubber may be as much as 100 wt %,although the polybutadiene content can be set to not more than 95 wt %,or in some cases to not more than 90 wt %.

In addition to the above-described polybutadiene, the base rubberserving as component A may include also other polybutadienes, such aspolybutadienes prepared using a group VIII metal compound catalyst, andother diene rubbers, some examples of which are styrene-butadienerubber, natural rubber, isoprene rubber and ethylene-propylene-dienerubber.

Of the rubber ingredients other than the above-described polybutadiene,the use of a second polybutadiene prepared using a group VIII catalystand having a Mooney viscosity (ML₁₊₄ (100° C.)) of less than 50 and aviscosity η at 25° C., as a 5 wt % toluene solution, of at least 200mPa·s but not more than 400 mPa·s is preferable for achieving a rubbercomposition having a good workability and a solid core having a highresilience.

Group VIII catalysts that may be used include nickel catalysts andcobalt catalysts.

Examples of suitable nickel catalysts include single-component systemssuch as nickel-kieselguhr, binary systems such as Raney nickel/titaniumtetrachloride, and ternary systems such as nickelcompound/organometallic compound/boron trifluoride etherate. Exemplarynickel compounds include reduced nickel on a carrier, Raney nickel,nickel oxide, nickel carboxylate and organonickel complex salts.Exemplary organometallic compounds include trialkylaluminum compoundssuch as triethylaluminum, tri-n-propylaluminum, triisobutylaluminum andtri-n-hexylaluminum; alkyllithium compounds such as n-butyllithium,sec-butyllithium, tert-butyllithium and 1,4-dilithiumbutane; anddialkylzinc compounds such as diethylzinc and dibutylzinc.

Examples of suitable cobalt catalysts include the following composed ofcobalt or cobalt compounds: Raney cobalt, cobalt chloride, cobaltbromide, cobalt iodide, cobalt oxide, cobalt sulfate, cobalt carbonate,cobalt phosphate, cobalt phthalate, cobalt carbonyl, cobaltacetylacetonate, cobalt diethyldithiocarbamate, cobalt anilinium nitriteand cobalt dinitrosyl chloride. It is particularly advantageous to usethese compounds in combination with, for example, a dialkylaluminummonochloride such as diethylaluminum monochloride or diisobutylaluminummonochloride; a trialkylaluminum such as triethylaluminum,tri-n-propylaluminum, triisobutylaluminum or tri-n-hexylaluminum; analkylaluminum sesquichloride such as ethylaluminum sesquichloride; oraluminum chloride.

Polymerization using the group VIII catalysts described above, andespecially a nickel or cobalt catalyst, can generally be carried out bya process in which the catalyst is continuously charged into the reactortogether with a solvent and the butadiene monomer. The reactionconditions are suitably selected from a temperature range of 5 to 60° C.and a pressure range of atmospheric pressure to 70 plus atmospheres, soas to yield a product having the above-indicated Mooney viscosity.

The second polybutadiene has a Mooney viscosity of less than 50,preferably not more than 48, and most preferably not more than 45. It isadvantageous for the lower limit in the Mooney viscosity to be at least10, preferably at least 20, more preferably at least 25, and mostpreferably at least 30.

The second polybutadiene has a viscosity η at 25° C., as a 5 wt %solution in toluene, of at least 200 mPa·s, preferably at least 210mPa·s, more preferably at least 230 mPa·s, and most preferably at least250 mPa·s, but not more than 400 mPa·s, preferably not more than 370mPa·s, more preferably not more than 340 mPa·s, and most preferably notmore than 300 mPa·s.

In the invention, the “viscosity η at 25° C. as a 5 wt % solution intoluene” (in mPa·s) refers to the value obtained by dissolving 2.28 g ofthe polybutadiene to be measured in 50 ml of toluene and using as thereference fluid a standard fluid for viscometer calibration (JIS Z8809)to carry out measurement at 25° C. with the requisite viscometer.

The second polybutadiene is typically included in the base rubber in anamount of 0% or more, preferably at least 5%, and more preferably atleast 10% by weight, but not more than 40%, preferably not more than30%, even more preferably not more than 20%, and most preferably notmore than 15% by weight.

Component B in the invention is an unsaturated carboxylic acid and/or anunsaturated carboxylic acid metal salt. Examples of suitable unsaturatedcarboxylic acids include acrylic acid, methacrylic acid, maleic acid andfumaric acid. Acrylic acid and methacrylic acid are especiallypreferred. Examples of suitable unsaturated carboxylic acid metal saltsinclude zinc salts and magnesium salts. Of these, zinc acrylate isespecially preferred.

The amount of the unsaturated carboxylic acid and/or unsaturatedcarboxylic acid metal salt (component B) per 100 parts by weight(sometimes abbreviated hereinafter as “parts”) of the base rubberserving as component A is generally at least 10 parts, preferably atleast 15 parts, and most preferably at least 20 parts, but generally notmore than 60 parts, preferably not more than 50 parts, more preferablynot more than 45 parts, and most preferably not more than 40 parts.

Component C in the invention is an organic sulfur compound. Exemplaryorganic sulfur compounds include thiophenols, thionaphthols, halogenatedthiophenols, and metal salts thereof. Specific examples includepentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol,p-chlorothiophenol, and the zinc salts thereof; diphenylpolysulfides,dibenzylpolysulfides, dibenzoylpolysulfides, dibenzothiazoylpolysulfidesand dithiobenzoylpolysulfides having 2 to 4 sulfurs;alkylphenyldisulfides, furan ring-bearing sulfur compounds and thiophenering-bearing sulfur compounds. Diphenyldisulfide and the zinc salt ofpentachlorothiophenol are especially preferred.

The amount of component C per 100 parts of the base resin serving ascomponent A is generally at least 0.1 part, preferably at least 0.2part, more preferably at least 0.4 part, and most preferably at least0.7 part, but generally not more than 5 parts, preferably not more than4 parts, more preferably not more than 3 parts, even more preferably notmore than 2 parts, and most preferably not more than 1.5 parts. Toolittle component C may fail to provide a resilience-improving effect,whereas too much component C may result in an excessively low corehardness and thus insufficient resilience.

Component D in the invention is an inorganic filler, illustrativeexamples of which include zinc oxide, barium sulfate and calciumcarbonate. The amount of component D per 100 parts of component A isgenerally at least 5 parts, preferably at least 7 parts, more preferablyat least 10 parts, and most preferably at least 13 parts, but generallynot more than 80 parts, preferably not more than 65 parts, morepreferably not more than 50 parts, and most preferably not more than 40parts. The use of too much or too little component D may make itimpossible to achieve a golf ball having the proper weight and adesirable rebound.

The organic peroxide used as component E in the invention may be asingle organic peroxide, although the use of a combination of two ormore organic peroxides is preferred. If (a) represents the organicperoxide having the shortest half-life at 155° C., (b) represents theorganic peroxide having the longest half-life at 155° C., and thehalf-lives of (a) and (b) are denoted as a_(t) and b_(t) respectively,it is desirable for the half-life ratio b_(t)/a_(t) to be at least 7,preferably at least 8, more preferably at least 9, and most preferablyat least 10, but not more than 20, preferably not more than 18, and mostpreferably not more than 16. Even with the use of two or more organicperoxides, at a half-life ratio outside of the above range, the desiredlevels of ball rebound, compression and durability may not be achieved.

It is desirable for (a) to have a half-life a_(t) at 155° C. of at least5 seconds, preferably at least 10 seconds, and most preferably at least15 seconds, but not more than 120 seconds, preferably not more than 90seconds, and most preferably not more than 60 seconds. It is desirablefor (b) to have a half-life b_(t) at 155° C. of at least 300 seconds,preferably at least 360 seconds, and most preferably at least 420seconds, but not more than 800 seconds, preferably not more than 700seconds, and most preferably not more than 600 seconds.

Specific examples of suitable organic peroxides include dicumylperoxide, 1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane andα,α′-bis(t-butylperoxy)diisopropylbenzene. These organic peroxides maybe commercially available products, such as Percumil D (available fromNOF Corporation), Perhexa 3M (NOF Corporation) and Luperco 231XL(available from Atochem Co.). The use of1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane as above organicperoxide (a) and dicumyl peroxide as above organic peroxide (b) ispreferred.

The overall amount of organic peroxide used as component E, per 100parts of component A, is at least 0.1 part, preferably at least 0.2part, more preferably at least 0.3 part, and most preferably at least0.4 part, but nor more that 0.8 part, preferably not more than 0.7 part,more preferably not more than 0.6 part, and most preferably not morethan 0.5 part. Too little organic peroxide increases the time requiredfor crosslinking, substantially lowering productivity during manufactureof the golf ball and also lowering compression by the ball. On the otherhand, too much organic peroxide lowers the rebound and durability of theball.

The amount of organic peroxide (a) included in the solid core per 100parts of component A is preferably at least 0.05 part, more preferablyat least 0.08 part, and most preferably at least 0.1 part, butpreferably not more than 0.5 part, more preferably not more than 0.4part, and most preferably not more than 0.3 part. The amount of organicperoxide (b) included per 100 parts of component A is preferably atleast 0.05 part, more preferably at least 0.15 part, and most preferablyat least 0.2 part, but preferably not more than 0.7 part, morepreferably not more than 0.6 part, and most preferably not more than 0.5part.

If necessary, the rubber composition may also include an antioxidant inan amount, per 100 parts of component A, of at least 0.05 part,preferably at least 0.1 part, and more preferably at least 0.2 part, butnot more than 3 parts, preferably not more than 2 parts, more preferablynot more than 1 part, and most preferably not more than 0.5 part. Theantioxidant may be a commercially available product, such as NocracNS-6, Nocrac NS-30 (both made by Ouchi Shinko Chemical Industry Co.,Ltd.), and Yoshinox 425 (made by Yoshitomi Pharmaceutical Industries,Ltd.).

The molded and vulcanized core of the inventive golf ball can beobtained by vulcanizing and curing the above-described rubbercomposition using a method of the same type as that used with known golfball rubber compositions. For example, vulcanization may be carried outat a temperature of 100 to 200° C. for a period of 10 to 40 minutes.

In the practice of the invention, the above golf ball core has ahardness which can be adjusted as appropriate for the intended use ofthe golf ball and is not subject to any particular limitation. That is,the molded core may have a cross-sectional hardness profile which isflat from the center to the surface of the core, or which varies fromthe center to the surface. Specifically, the molded core must have adeflection, when subjected to a load of 980 N (100 kg), of at least 2.5mm, preferably at least 2.7 mm, and most preferably at least 3.0 mm, butnot more than 6.0 mm, preferably not more than 5.5 mm, and mostpreferably not more than 5.0 mm. A core which is too hard and has toosmall a deflection will worsen the feel of the golf ball upon impactand, particularly on long shots such as with a driver in which the ballincurs a large deformation, will subject the ball to an excessiveincrease in spin, reducing the carry. On the other hand, when the coreis too soft, the golf ball will have a less lively feel when hit and asmaller rebound that shortens its carry, and will also have a poordurability to cracking with repeated impact.

The core has a diameter of at least 30.0 mm, and preferably at least32.0 mm, but not more than 40.0 mm, and preferably not more than 39.0mm.

It is recommended that the core have a specific gravity of generally atleast 0.9, preferably at least 1.0, and most preferably at least 1.1,but not more than 1.4, preferably not more than 1.3, and most preferablynot more than 1.2.

The multi-piece solid golf ball of the invention has a mantle of atleast one layer which encloses the above-described core, and also has acover which encloses the mantle. If the inventive ball is a four-piecesolid golf ball, the mantle is composed of two layers: an inner layerand an outer layer.

The mantle is made of a thermoplastic resin, and at least one layerthereof is composed of material [I] or [II] below.

[I] A mixture comprising as essential components:

-   -   at least 100 parts by weight of resin components which include a        base resin of (M) an olefin/unsaturated carboxylic acid binary        random copolymer and/or a metal ion neutralization product        thereof and (N) an olefin/unsaturated carboxylic        acid/unsaturated carboxylic acid ester ternary random copolymer        and/or a metal ion neutralization product thereof in a weight        ratio M/N of 100:0 to 25:75, in combination with (P) a        non-ionomeric thermoplastic elastomer in a weight ratio (M+N)/P        of 100:0 to 50:50;    -   (Q) 5 to 80 parts by weight of a fatty acid and/or fatty acid        derivative having a molecular weight of 280 to 1,500; and    -   (R) 0.1 to 10 parts by weight of a basic inorganic metal        compound capable of neutralizing un-neutralized acid groups in        the base resin and component Q.        [II] A mixture comprising as essential components:    -   resin components which include at least one base resin selected        from the group consisting of (M) olefin/unsaturated carboxylic        acid binary random copolymers and metal ion neutralization        products thereof and (N) olefin/unsaturated carboxylic        acid/unsaturated carboxylic acid ester ternary random copolymers        and metal ion neutralization products thereof, in combination        with (P) a non-ionomeric thermoplastic elastomer in a weight        ratio (M+N)/P of 100:0 to 50:50;    -   (Q) a fatty acid and/or fatty acid derivative having a molecular        weight of 280 to 1,500;    -   (R) a metal ion source capable of neutralizing un-neutralized        acid groups in the base resin and component Q; and    -   (S) a compound having a molecular weight of not more than 20,000        which bears at least two reactive functional groups.

In material [I], the olefins in the above base resin, both in componentM and component N, have a number of carbons that is generally at least2, but not more than 8, and preferably not more than 6. Suitableexamples include ethylene, propylene, butene, pentene, hexene, hepteneand octene. Ethylene is especially preferred.

Illustrative examples of the unsaturated carboxylic acid include acrylicacid, methacrylic acid, maleic acid and fumaric acid. Acrylic acid andmethacrylic acid are especially preferred.

The unsaturated carboxylic acid ester is preferably a lower alkyl esterof the unsaturated carboxylic acid. Specific examples include methylmethacrylate, ethyl methacrylate, propyl methacrylate, butylmethacrylate, methyl acrylate, ethyl acrylate, propyl acrylate and butylacrylate. Butyl acrylate (n-butyl acrylate, i-butyl acrylate) isespecially preferred.

The olefin/unsaturated carboxylic acid binary random copolymer ofcomponent M and the olefin/unsaturated carboxylic acid/unsaturatedcarboxylic acid ester ternary random copolymer of component N (thecopolymers in components M and N are hereinafter referred tocollectively as “random copolymers”) can each be obtained by suitablyformulating the above constituents and using a known method to carry outrandom copolymerization.

It is recommended that these random copolymers be prepared such as tohave a specific unsaturated carboxylic acid content (sometimes referredto hereinafter as the “acid content”). The amount of unsaturatedcarboxylic acid included within the random copolymer of component M isgenerally at least 4 wt %, preferably at least 6 wt %, more preferablyat least 8 wt %, and most preferably at least 10 wt %, but generally notmore than 30 wt %, preferably not more than 20 wt %, more preferably notmore than 18 wt %, and most preferably not more than 15 wt %.

Similarly, it is recommended that the amount of unsaturated carboxylicacid included within the random copolymer of component N be generally atleast 4 wt %, preferably at least 6 wt %, and most preferably at least 8wt %, but not more than 15 wt %, preferably not more than 12 wt %, andmost preferably not more than 10 wt %. If the random copolymers have toolow an acid content, the rebound of the ball may decline. On the otherhand, too high an acid content may lower the processability of thematerial.

The metal ion neutralization product of an olefin/unsaturated carboxylicacid binary random copolymer in component M and the metal ionneutralization product of an olefin/unsaturated carboxylicacid/unsaturated carboxylic acid ester ternary random copolymer incomponent N (the metal ion neutralization products of random copolymersin components M and N are hereinafter referred to collectively as “metalion-neutralized random copolymers”) can be obtained by partiallyneutralizing the acid groups on the random copolymer with metal ions.

Illustrative examples of metal ions for neutralizing the acid groupsinclude Na⁺, K⁺, Li⁺, Zn²⁺, Cu²⁺, Mg²⁺, Ca²⁺, Co²⁺, Ni²⁺ and Pb²⁺.Preferred metal ions include Na⁺, Li⁺, Zn²⁺ and Mg²⁺. The use of Zn²⁺ isespecially recommended.

The metal ion-neutralized random copolymers may be prepared byneutralization of the above random copolymers with the above metal ions.For example, use may be made of a neutralization method that involvesthe use of compounds such as the formates, acetates, nitrates,carbonates, bicarbonates, oxides, hydroxides or alkoxides of the abovemetal ions. The degree of neutralization of the random copolymer bythese metal ions is not subject to any particular limitation.

In this invention, the metal ion-neutralized random copolymers arepreferably zinc ion-neutralized ionomer resins. Such ionomer resinsincrease the melt flow rate of the material, facilitate adjustment tothe subsequently described optimal melt flow rate, and thus enable themoldability to be improved.

Commercial products may be used in the base resin made up of abovecomponents M and N. Examples of commercial products that may be used asthe random copolymer in component M include Nucrel 1560, Nucrel 1214 andNucrel 1035 (all products of DuPont-Mitsui Polychemicals Co., Ltd.); andEscor 5200, Escor 5100 and Escor 5000 (all products of ExxonMobilChemical). Examples of commercial products that may be used as therandom copolymer in component N include Nucrel AN4311 and Nucrel AN4318(both products of DuPont-Mitsui Polychemicals Co., Ltd.); and EscorATX325, Escor ATX320 and Escor ATX310 (all products of ExxonMobilChemical).

Examples of commercial products that may be used as the metalion-neutralized random copolymer in component M include Himilan 1554,Himilan 1557, Himilan 1601, Himilan 1605, Himilan 1706 and HimilanAM7311 (all products of DuPont-Mitsui Polychemicals Co., Ltd.), Surlyn7930 (produced by E.I. DuPont de Nemours and Co., Inc.) and Iotek 3110and Iotek 4200 (both products of ExxonMobil Chemical). Examples ofcommercial products that may be used as the metal ion-neutralized randomcopolymer in component N include Himilan 1855, Himilan 1856 and HimilanAM7316 (all products of DuPont-Mitsui Polychemicals Co., Ltd.), Surlyn6320, Surlyn 8320, Surlyn 9320 and Surlyn 8120 (all products of E.I.DuPont de Nemours and Co., Inc.), and Iotek 7510 and Iotek 7520 (bothproducts of ExxonMobil Chemical). Examples of zinc-neutralized ionomerresins that can be preferably used as the above metal ion-neutralizedrandom copolymers include Himilan 1706, Himilan 1557 and Himilan AM7316.

When the above-described base resin is prepared, the weight ratio M/N ofcomponent M to component N must be set at from 100:0 to 25:75,preferably from 100:0 to 50:50, more preferably from 100:0 to 75:25, andmost preferably 100:0. Too little component M lowers the resilience ofthe molded material.

In addition, the moldability can be further improved by adjusting therelative proportions of random copolymer and metal ion-neutralizedrandom copolymer in the base resin of above components M and N. It isrecommended that the ratio of random copolymer to metal ion-neutralizedrandom copolymer be generally from 0:100 to 60:40, preferably from 0:100to 40:60, more preferably from 0:100 to 20:80, and most preferably0:100. The presence of too much random copolymer may lower theprocessability during mixing.

Component P is a non-ionomeric thermoplastic elastomer which isoptionally included to further enhance both the feel of the golf ballupon impact and its rebound characteristics. In the invention, theabove-described base resin and component P are referred to collectivelyas the “resin components.” Specific examples of non-ionomericthermoplastic elastomers that may be used as component P include olefinelastomers, styrene elastomers, polyester elastomers, urethaneelastomers and polyamide elastomers. The use of an olefin elastomer or apolyester elastomer is preferred for increasing resilience.

Examples of commercial products that may be used as component P includeolefin elastomers such as Dynaron (manufactured by JSR Corporation) andpolyester elastomers such as Hytrel (manufactured by DuPont-Toray Co.,Ltd.).

It is recommended that the amount of component P per 100 parts by weightof the base resin in the material be generally 0 part or more,preferably at least 1 part, more preferably at least 2 parts, even morepreferably at least 3 parts, and most preferably at least 4 parts, butnot more than 100 parts, preferably not more than 60 parts, morepreferably not more than 40 parts, and most preferably not more than 20parts. Too much component P may lower the compatibility of the mixtureand markedly compromise the durability of the golf ball.

Next, component Q is a fatty acid or fatty acid derivative having amolecular weight of 280 to 1,500. This component has a very lowmolecular weight compared with the base resin and is used to adjust themelt viscosity of the mixture to a suitable level, particularly to helpimprove flow. Component Q has a relatively high content of acid groups(or derivatives thereof) and can prevent an excessive loss ofresilience.

The molecular weight of the fatty acid or fatty acid derivative ofcomponent Q is at least 280, preferably at least 300, more preferably atleast 330, and most preferably at least 360, but not more than 1,500,preferably not more than 1,000, more preferably not more than 600, andmost preferably not more than 500. Too low a molecular weight mayprevent a better heat resistance from being achieved, whereas too high amolecular weight may make it impossible to improve flow.

Preferred examples of the fatty acid or fatty acid derivative serving ascomponent Q include unsaturated fatty acids having a double bond ortriple bond on the alkyl group as well as derivatives thereof, andsaturated fatty acids in which all the bonds on the alkyl group aresingle bonds as well as derivatives thereof. It is recommended that thenumber of carbons on the molecule be generally at least 18, preferablyat least 20, more preferably at least 22, and most preferably at least24, but not more than 80, preferably not more than 60, more preferablynot more than 40, and most preferably not more than 30. Too few carbonsmay prevent a better heat resistance from being achieved and may alsomake the content of acid groups so high as to diminish theflow-enhancing effect on account of interactions between acid groups incomponent Q and acid groups present in the base resin. On the otherhand, too many carbons increases the molecular weight, which may alsoprevent the desired flow-enhancing effect from being achieved.

Specific examples of fatty acids that may be used as component Q includestearic acid, 12-hydroxystearic acid, behenic acid, oleic acid, linoleicacid, linolenic acid, arachidic acid and lignoceric acid. Of these,stearic acid, arachidic acid, behenic acid and lignoceric acid arepreferred. Behenic acid is especially preferred.

Fatty acid derivatives which may be used as component Q include metallicsoaps in which the proton on the acid group of the fatty acid has beensubstituted with a metal ion. Metal ions that may be used in suchmetallic soaps include Na⁺, Li⁺, Ca²⁺, Mg²⁺, Zn²⁺, Mn²⁺, Al³⁺, Ni²⁺,Fe²⁺, Fe³⁺, Cu²⁺, Sn ²⁺, Pb²⁺ and Co²⁺. Of these, Ca²⁺, Mg²⁺ and Zn²⁺are preferred.

Specific examples of fatty acid derivatives that may be used ascomponent Q include magnesium stearate, calcium stearate, zinc stearate,magnesium 12-hydroxystearate, calcium 12-hydroxystearate, zinc12-hydroxystearate, magnesium arachidate, calcium arachidate, zincarachidate, magnesium behenate, calcium behenate, zinc behenate,magnesium lignocerate, calcium lignocerate and zinc lignocerate. Ofthese, magnesium stearate, calcium stearate, zinc stearate, magnesiumarachidate, calcium arachidate, zinc arachidate, magnesium behenate,calcium behenate, zinc behenate, magnesium lignocerate, calciumlignocerate and zinc lignocerate are preferred.

Alternatively, it is possible to use in the invention, as thecombination of the base resin (above components M and N) with abovecomponent Q, a known metallic soap-modified ionomer, including thosedescribed in U.S. Pat. No. 5,312,857, U.S. Pat. No. 5,306,760 andInternational Application WO 98/46671.

Component R is a basic inorganic metal compound which can neutralizeacid groups in the base resin and component Q. When a metallicsoap-modified ionomer resin (e.g., the metallic soap-modified ionomerresins mentioned in the above-cited prior-art patent publications) isused alone without including component R, the metallic soap and theun-neutralized acid groups present on the ionomer resin undergo exchangereactions during mixture under heating, generating a large amount offatty acid. Because the fatty acid has a low thermal stability andreadily vaporizes during molding, it may cause molding defects.Moreover, it adheres to the surface of the molded article, which cansubstantially lower paint film adhesion.

Accordingly, a basic inorganic metal compound (component R) whichneutralizes acid groups present in the base resin and in component Q isincluded as an essential ingredient in order to improve the resilienceof the molded mantle layer.

That is, incorporating above component R in the material [I] results ina suitable degree of neutralization of the acid groups in the base resinand in component Q. Moreover, optimizing the various components in thisway produces synergistic effects which increase the thermal stability ofthe mixture, impart a good processability and make it possible toenhance the resilience.

It is recommended that the basic inorganic metal compound used ascomponent R be one which has a high reactivity with the base resin andincludes no organic acids in the reaction by-products, thus enabling thedegree of neutralization of the mixture to be increased without a lossof thermal stability.

Illustrative examples of the metal ions in the basic inorganic metalcompound serving as component R include Li⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺, Zn²⁺,Al³⁺, Ni²⁺, Fe²⁺, Fe³⁺, Cu²⁺, Mn²⁺, Sn²⁺, Pb²⁺ and Co²⁺. Known basicinorganic fillers containing these metal ions may be used as the basicinorganic metal compound. Specific examples include magnesium oxide,magnesium hydroxide, magnesium carbonate, zinc oxide, sodium hydroxide,sodium carbonate, calcium oxide, calcium hydroxide, lithium hydroxideand lithium carbonate. A hydroxide or a monoxide is recommended. Calciumhydroxide and magnesium oxide, both of which have a high reactivity withthe base resin, are preferred. Calcium hydroxide is especiallypreferred.

Because the above-described material [I] is arrived at by blendingspecific respective amounts of components Q and R with the resincomponents, i.e., the base resin containing specific respective amountsof components M and N in combination with optional component P, thismaterial [I] has excellent thermal stability, flow properties andmoldability, and can impart the molded layer with a markedly improvedresilience.

Components Q and R are compounded in respective amounts, per 100 partsby weight of the resin components suitably formulated from components M,N and P, of at least 5 parts by weight, preferably at least 10 parts byweight, more preferably at least 15 parts by weight, and most preferablyat least 18 parts by weight, but not more than 80 parts by weight,preferably not more than 40 parts by weight, more preferably not morethan 25 parts by weight, and most preferably not more than 22 parts byweight, of component Q; and at least 0.1 part by weight, preferably atleast 0.5 part by weight, more preferably at least 1 part by weight, andmost preferably at least 2 parts by weight, but not more than 10 partsby weight, preferably not more than 8 parts by weight, more preferablynot more than 6 parts by weight, and most preferably not more than 5parts by weight, of component R. Too little component Q lowers the meltviscosity, resulting in inferior processability, whereas too much lowersthe durability. Too little component R fails to improve thermalstability and resilience, whereas too much instead lowers the heatresistance of the golf ball-forming material due to the presence ofexcess basic inorganic metal compound.

In the above-described material [I] which is preferably formulated fromthe respective above-indicated amounts of the foregoing resin componentsand components Q and R, it is recommended that at least 50 mol %,preferably at least 60 mol %, more preferably at least 70 mol %, andmost preferably at least 80 mol %, of the acid groups be neutralized. Ahigh degree of neutralization such as this makes it possible to morereliably suppress the exchange reactions that cause trouble when only abase resin and a fatty acid or fatty acid derivative are used as in theabove-cited prior art, thus preventing the formation of fatty acid. As aresult, there is obtained a material of greatly increased thermalstability and good processability which can provide a molded layer ofmuch better resilience than prior-art ionomer resins.

“Degree of neutralization,” as used above, refers to the degree ofneutralization of acid groups present within the mixture of the baseresin and the fatty acid or fatty acid derivative serving as componentQ, and differs from the degree of neutralization of the ionomer resinitself when an ionomer resin is used as the metal ion-neutralized randomcopolymer in the base resin. A mixture according to the invention havinga certain degree of neutralization, when compared with an ionomer resinalone having the same degree of neutralization, contains a very largenumber of metal ions. This large number of metal ions increases thedensity of ionic crosslinks which contribute to improved resilience,making it possible to confer the molded layer with excellent resilience.

To more reliably achieve a material [I] having both a high degree ofneutralization and good flow properties, it is recommended that the acidgroups in the above-described mixture be neutralized with transitionmetal ions and with alkali metal and/or alkaline earth metal ions.Although transition metal ions have a weaker ionic cohesion than alkalimetal and alkaline earth metal ions, the combined use of these differenttypes of ions to neutralize acid groups in the mixture can provide asubstantial improvement in the flow properties.

It is recommended that the molar ratio between the transition metal ionsand the alkali metal and/or alkaline earth metal ions be within a rangeof generally 10:90 to 90:10, preferably 20:80 to 80:20, more preferably30:70 to 70:30, and most preferably 40:60 to 60:40. Too low a molarratio of transition metal ions may fail to provide sufficientimprovement in the flow properties of the material. On the other hand, atransition metal ion molar ratio that is too high may lower theresilience of the mantle.

Specific, non-limiting, examples of the metal ions include zinc ions asthe transition metal ions and at least one type of ion selected fromamong sodium, lithium and magnesium ions as the alkali metal or alkalineearth metal ions.

A known method may be used to obtain a mixture in which the desiredamount of acid groups have been neutralized with transition metal ionsand alkali metal or alkaline earth metal ions. Specific examples ofmethods of neutralization with transition metal ions, particularly zincions, include the use of zinc soaps as the fatty acid derivative, theuse of zinc ion-neutralized products (e.g., zinc ion-neutralized ionomerresins) when formulating component M and component N as the base resin,and the use of zinc compounds such as zinc oxide as the basic inorganicmetal compound of component R.

The above-described material [I] may include also suitable amounts ofany additives that may be required for the intended use of the material.For example, if the material is to be used as a cover stock, suchadditives as pigments, dispersants, antioxidants, ultraviolet absorbersand light stabilizers may be added to the essential ingredientsdescribed above. When such additives are included in the composition,they may be incorporated in an amount, per 100 parts by weight of theessential ingredients of material [I] (the resin components andcomponents Q and R), of preferably at least 0.1 part by weight, morepreferably at least 0.5 part by weight, and most preferably at least 1part by weight, but not more than 10 parts by weight, preferably notmore than 6 parts by weight, and most preferably not more than 4 partsby weight.

The foregoing material [I] may be obtained by preparing a mixture of theabove-described essential ingredients and whatever optional ingredientsmay be needed, then heating and working the mixture under suitableconditions, such as a heating temperature of 150 to 250° C. and using aninternal mixer such as a kneading-type twin-screw extruder, a Banburymixer or a kneader. Any suitable method may be used without particularlimitation to blend various additives with the above essentialingredients of the invention. For example, the additives may be combinedwith the essential ingredients, and heating and mixture of all theingredients carried out at the same time. Alternatively, the essentialingredients may first be heated and mixed, following which the optionaladditives may be added and the overall composition subjected toadditional heating and mixture.

This material [I] should have a melt flow rate adjusted to ensure flowproperties that are particularly suitable for injection molding and thusimprove moldability. Specifically, it is recommended that the melt flowrate, as measured according to JIS-K7210 at a temperature of 190° C. andunder a load of 21.18 N (2.16 kgf), be set to generally at least 0.5dg/min, preferably at least 1 dg/min, more preferably at least 1.5dg/min, and even more preferably at least 2 dg/min, but generally notmore than 20 dg/min, preferably not more than 10 dg/min, more preferablynot more than 5 dg/min, and most preferably not more than 3 dg/min. Toolarge or small a melt flow rate may result in a marked decline in meltprocessability.

It is preferable also for material [I] to have, in infrared absorptionspectroscopy, an appropriate absorbance at the absorption peakattributable to carboxylate anion stretching vibrations normallydetected at 1530 to 1630 cm⁻¹ relative to the absorbance at theabsorption peak attributable to carbonyl stretching vibrations normallydetected at 1690 to 1710 cm⁻¹. For the sake of clarity, this ratio maybe expressed as follows: (absorbance of absorption peak for carboxylateanion stretching vibrations)/(absorbance of absorption peak for carbonylstretching vibrations).

Here, “carboxylate anion stretching vibrations” refers to vibrations bycarboxyl groups from which the proton has dissociated (metalion-neutralized carboxyl groups), whereas “carbonyl stretchingvibrations” refers to vibrations by undissociated carboxyl groups. Theratio between these respective peak intensities depends on the degree ofneutralization. In the ionomer resins having a degree of neutralizationof about 50 mol % which are commonly used, the ratio between these peakabsorbances is about 1:1.

To improve the thermal stability, flow, processability and resilience ofthe material [I] used in the invention, it is recommended that thematerial have a carboxylate anion stretching vibration peak absorbancewhich is at least 1.3 times, preferably at least 1.5 times, and mostpreferably at least 2 times, the carbonyl stretching vibration peakabsorbance. The absence of any carbonyl stretching vibration peak isespecially preferred.

The thermal stability of material [I] can be measured bythermogravimetry. It is recommended that, in thermogravimetry, thecomposition have a weight loss at 250° C., based on the weight of thematerial at 25° C., of generally not more than 2 wt %, preferably notmore than 1.5 wt %, and most preferably not more than 1 wt %.

It is recommended that material [I] be formulated such that the moldedlayer obtained therefrom has a Durometer D hardness of generally atleast 50, preferably at least 53, more preferably at least 56, and mostpreferably at least 58, but preferably not more than 70, more preferablynot more than 65, and most preferably not more than 62. If the DurometerD hardness is too high, the resulting golf ball may have a markedlydiminished feel upon impact. On the other hand, too low a hardness mayreduce the rebound of the ball.

The specific gravity of material [I] is not subject to any particularlimitation, although it is recommended that the specific gravity begenerally at least 0.9 g/cm³, preferably at least 0.92 g/cm³, and mostpreferably at least 0.94 g/cm³, but not more than 1.2 g/cm³, preferablynot more than 1.1 g/cm³, and most preferably not more than 1.05 g/cm³.

Material [II] may include above components M, N, P, Q and R in the sametypes and amounts as are used in material [I]. However, material [II]differs from material [I] in that it may use either component M orcomponent N alone, or may use both together. If components M and N areboth included in material [II], they may be used in a weight ratio offrom 90:10 to 10:90, and particularly from 80:20 to 20:80.

Material [II] additionally includes, as component S, a compound whichhas a molecular weight of not more than 20,000 and bears at least tworeactive functional groups.

Exemplary compounds which have a molecular weight of not more than20,000 and bear at least two reactive functional groups includemonomers, oligomers and macromonomers which have a total of at least tworeactive functional groups of one or more types on each molecule and amolecular weight of not more than 20,000, and preferably not more than5,000. The number of reactive functional groups, while not subject toany particular upper limit, is generally 6 or less.

“Monomer” is used here in the usual sense of a compound employed as abasic building block in polymer synthesis. “Oligomer” refers to alow-molecular-weight product which is obtained from monomers commonlyemployed in polymer synthesis and which contains generally at least twomonomer units and has a molecular weight of up to several thousand.“Macromonomer” refers to a material which is an oligomer havingpolymerizable functional groups at the ends and which is employed in thesynthesis of graft polymers by the copolymerization of differentfunctional comonomers. Monomers, oligomers and macromonomers generallyserve as intermediates in the synthesis of plastics and elastomers, orare used as starting materials for the production of graft polymers.Notable use is being made recently of oligomers and macromonomers havingvarious functional groups.

The reactive functional groups are not subject to any particularlimitation, insofar as they are capable of improving adhesion betweenlayers of the golf ball. Preferred examples of reactive functionalgroups include hydroxyl groups, amino groups, carboxyl groups and epoxygroups. In the case of a blend with an ionomer resin, hydroxyl groupsare especially preferred because they have a limited impact on the meltflow rate.

Illustrative, non-limiting, examples of suitable monomers include1,3-butanediol, 1,6-hexanediol, trimethylolpropane, mannitol, sorbitoland polysaccharides. Illustrative, non-limiting examples of suitableoligomers and macromonomers include polyethylene glycol,polyhydroxypolyolefin oligomers, modified low-molecular-weightpolyethylene, modified low-molecular-weight polypropylene, modifiedlow-molecular-weight polystyrene and modified liquid rubber.Polyhydroxypolyblefin oligomers and trimethylolpropane are especiallypreferred. These may be used singly or in combinations of two typesthereof, as desired.

The above monomer, oligomer or macromonomer may be a commerciallyavailable product, such as trimethylolpropane produced by Mitsubishi GasChemical Co., Ltd. or the polyhydroxypolyolefin oligomers having 150 to200 backbone carbons and hydroxyl end groups produced under the tradename Polytail H by Mitsubishi Chemical Corporation.

The amount of compound having at least two reactive functional groupsincluded in material [II] per 100 parts by weight of the resincomponents is preferably 0.1 to 100 parts by weight, preferably 0.2 to50 parts by weight, more preferably 0.3 to 20 parts by weight, even morepreferably 0.4 to 10 parts by weight, and most preferably 0.5 to 5 partsby weight. If too little of this compound is included, the desiredeffects of addition may not be achieved. On the other hand, the additionof too much may lower the physical properties of the golf ball.

The foregoing material [II] may be obtained by preparing a mixture ofthe above-described essential ingredients and whatever optionalingredients may be needed, then heating and working the mixture undersuitable conditions, such as a heating temperature of 150 to 250° C. andusing an internal mixer such as a kneading-type twin-screw extruder, aBanbury mixer or a kneader. Any suitable method may be used withoutparticular limitation to blend various additives with the aboveessential ingredients of the invention. For example, the additives maybe combined with the essential ingredients, and heating and mixture ofall the ingredients carried out at the same time. Alternatively, theessential ingredients may first be heated and mixed, following which theoptional additives may be added and the overall composition subjected toadditional heating and mixture.

This material [II] should have a melt flow rate adjusted to ensure flowproperties that are particularly suitable for injection molding and thusimprove moldability. Specifically, it is recommended that the melt flowrate, as measured according to JIS-K7210 at a temperature of 190° C. andunder a load of 21.18 N (2.16 kgf), be set to generally at least 0.5dg/min, preferably at least 1 dg/min, more preferably at least 1.5dg/min, and even more preferably at least 2 dg/min, but generally notmore than 20 dg/min, preferably not more than 10 dg/min, more preferablynot more than 5 dg/min, and most preferably not more than 3 dg/min. Toolarge or small a melt flow rate may result in a marked decline in meltprocessability.

It is advantageous for material [II] to have a specific gravity of from0.9 to 1.2, preferably from 0.92 to 1.1, and most preferably from 0.93to 1.05.

Moreover, it is desirable for material [II] to have a Durometer Dhardness of at least 40, preferably at least 45, and most preferably atleast 50, but not more than 70, preferably not more than 65, and mostpreferably not more than 60.

This material [II] can impart good adhesion by virtue of the reaction ofreactive functional groups on component S with functional groups onother materials.

At least one layer of the mantle may be made primarily of athermoplastic polyester, suitable examples of which include thoseproduced by DuPont-Toray Co., Ltd. under the trade name Hytrel.

In particular, when the mantle is composed of two layers—an inner layerand an outer layer, to achieve a golf ball having both a soft feel uponimpact and a high rebound, it is desirable for either the inner layer orthe outer layer to be made primarily of the above-describedthermoplastic polyester and for the other layer to be made of material[I] or [II].

Regardless of whether the mantle is composed of a single layer or of twoor more layers, it is advantageous for each layer of the mantle to havea Durometer D hardness of at least 30, and preferably at least 35, butnot more than 70, and preferably not more than 65. To achieve a golfball having both a soft feel on impact and a high rebound, it isdesirable for the mantle layer in contact with the subsequentlydescribed golf ball cover to have a Durometer D hardness of at least 45,and preferably at least 50, but not more than 70, preferably not morethan 65, and most preferably not more than 63.

When the mantle is composed of an inner layer and an outer layer, asjust noted, it is preferable for the outer layer to have a Durometer Dhardness of 45 to 70. The inner layer of the mantle may have higher orlower hardness than the outer layer, although to ensure a soft feel uponimpact, it is desirable for the inner layer to be softer than the outerlayer.

Regardless of whether the mantle is composed of a single layer or of twoor more layers, each layer has a thickness of at least 0.5 mm, andpreferably at least 0.8 mm, but not more than 2.0 mm, and preferably notmore than 1.8 mm. If the mantle is composed of two or more layers (suchas an inner layer/outer layer construction), it is desirable for theoverall mantle thickness to be at least 1.0 mm, and preferably at least1.5 mm, but not more than 4.0 mm, and preferably not more than 3.5 mm.

The cover of the inventive golf ball is composed primarily of athermoplastic polyurethane formulated at least in part of the followingmaterial G.

(G) Thermoplastic Polyurethane Material

The thermoplastic polyurethane material has a structure which iscomposed of soft segments made of a polymeric polyol (polymeric glycol),hard segments made of a chain extender, and a diisocyanate. Here, thepolymeric polyol used as a starting material is not subject to anyparticular limitation, and may be any that is used in the prior artrelating to thermoplastic polyurethane materials. Exemplary polymericpolyols include polyester polyols and polyether polyols, althoughpolyether polyols are better than polyester polyols for synthesizingthermoplastic polyurethane materials having a high resilience andexcellent low-temperature properties. Suitable polyether polyols includepolytetramethylene glycol and polypropylene glycol. Polytetramethyleneglycol is especially preferred for achieving a good resilience and goodlow-temperature properties. The polymeric polyol has an averagemolecular weight of preferably 1,000 to 5,000. To synthesize athermoplastic polyurethane material having a high resilience, an averagemolecular weight of 2,000 to 4,000 is especially preferred.

Preferred chain extenders include those used in the prior art relatingto thermoplastic polyurethane materials. Illustrative, non-limiting,examples include 1,4-butylene glycol, 1,2-ethylene glycol,1,3-butanediol, 1,6-hexanediol and 2,2-dimethyl-1,3-propanediol. Thesechain extenders have an average molecular weight of preferably 20 to15,000.

Preferred diisocyanates include those used in the prior art relating tothermoplastic polyurethane materials. Illustrative, non-limiting,examples include aromatic diisocyanates such as 4,4′-diphenylmethanediisocyanate, 2,4-toluene diisocyanate and 2,6-toluene diisocyanate; andaliphatic diisocyanates such as hexamethylene diisocyanate. Depending onthe type of isocyanate used, the crosslinking reaction during injectionmolding may be difficult to control. To ensure stability of the reactionbetween the thermoplastic polyurethane material G and the subsequentlydescribed isocyanate mixture H, it is most preferable to use4,4′-diphenylmethane diisocyanate.

Commercially available products may be suitably used as theabove-described thermoplastic polyurethane material. Illustrativeexamples include Pandex T8290, Pandex T8295 and Pandex T8260 (allmanufactured by DIC Bayer Polymer, Ltd.), and Resamine 2593 and Resamine2597 (both manufactured by Dainichi Seika Colour & Chemicals Mfg. Co.,Ltd.).

The above-described thermoplastic polyurethane material G may be used byitself. However, to further enhance the resilience and scuff resistanceof the cover, it is preferable for the cover to be made of a composition[III] consisting essentially of:

-   (G) the above-described thermoplastic polyurethane material, and-   (H) an isocyanate mixture obtained by dispersing (h1) an isocyanate    compound bearing as functional groups at least two isocyanate groups    per molecule in (h2) a thermoplastic resin which substantially does    not react with isocyanate.    (H) Isocyanate Mixture

The isocyanate mixture H is prepared by dispersing (h1) an isocyanatecompound bearing as functional groups at least two isocyanate groups permolecule in (h2) a thermoplastic resin which substantially does notreact with isocyanate. Preferred isocyanate compounds (h1) include thoseused in the prior art relating to thermoplastic polyurethane materials.Illustrative, non-limiting, examples include aromatic diisocyanates suchas 4,4′-diphenylmethane diisocyanate, 2,4-toluene diisocyanate and2,6-toluene diisocyanate; and aliphatic diisocyanates such ashexamethylene diisocyanate. To ensure good reactivity and good safetyduring production, it is most preferable to use 4,4′-diphenylmethanediisocyanate.

The above-described thermoplastic resin h2 is preferably a resin havinga low water absorption and excellent compatibility with thermoplasticpolyurethane materials. Illustrative examples of such resins includepolystyrene resins, polyvinyl chloride resins, ABS resins, polycarbonateresins, and polyester elastomers (e.g., polyetherester block copolymers,polyesterester block copolymers). For good resilience and strength,polyester elastomers, and especially polyetherester block copolymers,are preferred.

The weight ratio of the thermoplastic resin h2 to the isocyanatecompound h1 in the isocyanate mixture H is preferably from 100:5 to100:100, and most preferably from 100:10 to 100:40. If the amount ofisocyanate compound h1 relative to the amount of thermoplastic resin h2is too small, more isocyanate mixture H must be added to achieve anamount of addition sufficient for the crosslinking reaction with thethermoplastic polyurethane material G. As a result, the thermoplasticresin h2 exerts too large an influence, causing the composition [III] tohave inadequate properties. On the other hand, if the amount ofisocyanate is too large, the isocyanate compound h1 causes slippage tooccur during kneading, making the isocyanate mixture H difficult toprepare.

The isocyanate mixture H can be prepared by, for example, mixing theisocyanate compound h1 into the thermoplastic resin h2 and thoroughlykneading these together with mixing rollers or in a Banbury mixer at atemperature of 130 to 250° C., and either pelletizing the mixture orcooling then milling it. An example of a commercially available productthat may be suitably used as the isocyanate mixture H is Crossnate EM30(produced by Dainichi Seika Colour & Chemicals Mfg. Co., Ltd.).

Composition [III]

Composition [III] consists essentially of the thermoplastic polyurethanematerial G and isocyanate mixture H described above. The compositioncontains these components in a weight ratio of the thermoplasticpolyurethane material G to the isocyanate mixture H within a range ofpreferably 100:1 to 100:100, more preferably 100:5 to 100:50, and mostpreferably 100:10 to 100:30. If the amount of isocyanate mixture Hincluded in composition [III] relative to the thermoplastic polyurethanematerial G is too small, a sufficient degree of crosslinking will notoccur. On the other hand, if the amount of isocyanate mixture H is toolarge, unreacted isocyanate may cause discoloration of the molded golfball cover.

In addition to the above-described components, the cover stock maycontain also other ingredients, such as thermoplastic polymericmaterials other than thermoplastic polyurethane materials. Illustrativeexamples of such thermoplastic polymeric materials that may also be usedinclude polyester elastomers, polyamide elastomers, ionomer resins,styrene block elastomers, polyethylene and nylon resins. The amount inwhich such thermoplastic polymeric materials other than thermoplasticpolyurethane materials are included, per 100 parts by weight of thethermoplastic polyurethane material serving as the essential componenttherein, is generally 0 to 100 parts by weight, preferably 10 to 75parts by weight, and most preferably 10 to 50 parts by weight. Thisamount may be selected as appropriate for such purposes as adjusting thehardness and increasing the resilience of the molded cover, enhancingthe flow properties of the cover stock, and improving adhesion of thecover to the underlying mantle layer. If necessary, the cover stock mayhave added thereto various additives, such as pigments, dispersants,antioxidants, light stabilizers, ultraviolet absorbers and partingagents.

The cover on the inventive golf ball can be formed by, for example,adding an isocyanate mixture H to the thermoplastic polyurethanematerial G and dry mixing, then molding the resulting mixture around theball precursor (core+mantle) in an injection molding machine. Themolding temperature varies according to the type of thermoplasticpolyurethane material G, although molding is generally carried out at atemperature within a range of 150 to 250° C.

The reactions and crosslinking which take place in the golf ball coverobtained as described above are believed to involve the reaction ofisocyanate groups with hydroxyl groups remaining on the thermoplasticpolyurethane material to form urethane bonds, or addition reactions byisocyanate groups at the urethane groups on the thermoplasticpolyurethane to form allophanate or biuret crosslinks. Right after thethermoplastic polyurethane composition used as the cover stock isinjection molded, crosslinking has not yet proceeded to a sufficientdegree. However, the crosslinking reaction can be made to proceedfurther by carrying out an annealing step after molding, so as to ensurethat those characteristics useful in a golf ball cover are maintained.“Annealing,” as used herein, refers to heat aging the cover at aconstant temperature for a fixed length of time, or aging the cover fora fixed period at room temperature.

It is desirable for the cover material to have a surface hardness, asmeasured with a Shore Durometer using indenter D in accordance with JISK6253, of 40 to 60, preferably 43 to 60, and most preferably 45 to 55. Acover having too low a surface hardness may result in excessive backspinon shots taken with an iron, making the ball difficult to control. Onthe other hand, a cover having too high a surface hardness may result ina less than satisfactory back spin on shots with an iron, therebylowering controllability, and may also give the ball a poor feel onimpact.

It is desirable for the cover material to have a resilience, as measuredaccording to JIS-K7311, of at least 45%, preferably 45 to 85%, morepreferably 50 to 80%, and most preferably 50 to 60%. Thermoplasticpolyurethane materials are not materials known for having a particularlyoutstanding resilience, and so strict selection of the resilience isdesirable. A cover material having too low a resilience may result in asubstantial decline in the carry of the golf ball. On the other hand, acover material with too high a resilience may give the ball excessiveinitial velocity on shots of less than 100 yards that require goodcontrol and in putting, and may have a feel on impact that does notagree with the golfer.

The cover composed primarily of the above-described thermoplasticpolyurethane has a Durometer D hardness of at least 40, and preferablyat least 42, but not more than 60, and preferably not more than 58. Thiscover hardness is lower than the hardness of the mantle layer in contactwith the cover, thereby enhancing the spin characteristics on approachshots and softening the feel upon impact with a putter.

It is advantageous for the cover to have a Durometer D hardness Hc andthe mantle layer in contact with the cover to have a Durometer Dhardness Hi such that the difference Hi−Hc is at least 1, and preferablyat least 3, but not more than 20, and preferably not more than 15.

It is also advantageous for the cover to have a thickness of at least0.5 mm, and preferably at least 0.7 mm, but not more than 2.5 mm, andpreferably not more than 2.3 mm.

The golf ball of the invention can be manufactured in accordance withthe Rules of Golf for use in competitive play, in which case the ballmay be formed to a diameter of not less than 42.67 mm and a weight ofnot more than 45.93 g. It is recommended that the diameter of the golfball have an upper limit of preferably not more than 44.0 mm, morepreferably not more than 43.5 mm, and most preferably not more than 43.0mm. It is also recommended that the weight of the golf ball have a lowerlimit of preferably not less than 44.5 g, more preferably not less than45.0 g, even more preferably not less than 45.1 g, and most preferablynot less than 45.2 g.

It is desirable for the golf ball hardness to be such that, when theball is subjected to a load of 980 N (100 kgf), it undergoes adeflection of 2.0 to 4.0 mm, and preferably 2.2 to 3.8 mm.

The construction, composition of the respective layers and otherfeatures described in detail above provide the golf balls of theinvention with an excellent rebound.

EXAMPLES

The following examples and comparative examples are given by way ofillustration and not by way of limitation.

Examples 1 to 8, Comparative Examples 1 to 4

Golf ball cores of the diameters and hardnesses shown in Table 3 wereproduced by using the rubber compositions shown in Table 1 andvulcanizing at 155° C. for 17 minutes.

Next, in each example, a mantle inner layer and a mantle outer layer ofthe respective formulations shown in Table 2 were formed by injectionmolding. A cover was then injection molded over the mantle outer layer,thereby forming golf balls having the mantle and cover characteristicsshown in Table 3. The flight performance, spin performance, feel onimpact and scuff resistance of each of the golf balls thus obtained wereevaluated as described below. The results are given in Table 3.

-   Core and Ball Hardness: Measured as the deflection (mm) when    subjected to a load of 980 N (100 kg).-   Mantle and Cover Hardness: The Durometer D hardness, as measured in    accordance with JIS K6253.-   Flight Performance: The initial velocity, spin rate, carry and total    distance for each golf ball was measured when the ball was struck at    a head speed of 45 m/s (HS 45) with a driver (W#1) mounted on a    swing machine. The test was conducted at a temperature of 23° C. The    club used was a Tour Stage X500 made by Bridgestone Sports Co.,    Ltd., and having a loft angle of 9 degrees and an X shaft.-   Spin Performance on Approach Shot: The spin rate of the ball when    hit at a head speed of 20 m/s using a sand wedge (Tour Stage, made    by Bridgestone Sports Co., Ltd.) mounted on a swing machine was    measured. The test was conducted at a temperature of 23° C.-   Feel: The feel of each ball when hit with a driver (W#1) and a    putter was rated by five top-caliber amateur golfers as “soft” (most    desirable), “ordinary,” or “hard” (least desirable). The rating    assigned most often to a particular ball was used as that ball's    overall rating.-   Scuff Resistance: The ball was temperature conditioned to 23° C.,    then hit at a head speed of 33 m/s with a pitching wedge mounted on    a swing machine. After being hit, the ball was examined visually for    signs of damage. The scuff resistance was rated as follows.    -   Good: Damage was not observed, or was of such a limited degree        as to pose no impediment to further use of the ball.

Not good (NG): Considerable damage, such as surface scuffing and loss ofdimples. TABLE 1 Example Comparative Example Ingredients (pbw) 1 2 3 4 56 7 8 1 2 3 4 Polybutadiene HCBN-13 100 100 100 100 100 100 100 100 BR0150 50 50 50 BR11 50 50 50 50 Peroxide (a) Perhexa 0.3 0.3 0.3 0.3 0.30.3 0.3 0.3 0.6 0.6 0.6 0.6 3M-40 (b) Percumil D 0.3 0.3 0.3 0.3 0.3 0.30.3 0.3 0.6 0.6 0.6 0.6 Antioxidant Nocrac NS-6 0.1 0.1 0.1 0.1 0.1 0.100.1 0.1 0.1 0.1 0.1 0.1 Zinc oxide 20.94 20.94 22.35 20.94 22.35 21.720.94 25.2 20.94 20.24 20.94 19.5 Zinc acrylate 33.0 33.0 27.3 33.0 27.329.5 33.0 26.1 33.0 35.8 33.0 34.4 Zinc salt of 1.0 1.0 1.0 1.0 1.0 1.01.0 1.0 1.0 1.0 1.0 1.0 pentachlorothiophenol

-   BR01: A polybutadiene produced by JSR Corporation. Cis-1,4 unit    content, 96%. Mooney viscosity (ML₁₊₄ (100° C.)), 44. Polydispersity    Mw/Mn, 4.2. Catalyst, nickel. Solution viscosity, 150 mPa·s.-   BR11: A polybutadiene produced by JSR Corporation. Cis-1,4 unit    content, 96%. Mooney viscosity (ML₁₊₄ (100° C.)), 44. Polydispersity    Mw/Mn, 4.1. Catalyst, nickel. Solution viscosity, 270 mPa·s.-   HCBN-13: Produced by JSR Corporation. Cis-1,4 unit content, 96%.    Mooney viscosity (ML₁₊₄ (100° C.)), 53. Polydispersity Mw/Mn, 3.2.    Catalyst, neodymium.-   Perhexa 3M-40: Produced by NOF Corporation. Perhexa 3M-40 is a 40%    dilution. The amount of addition is the effective weight of the    1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane in the dilution    added.-   Percumil D: Produced by NOF Corporation. Dicumyl peroxide.

Nocrac NS-6: 2,2′-Methylenebis(4-methyl-6-t-butylphenol) produced byOuchi Shinko Chemical Industry Co., Ltd. TABLE 2 Example ComparativeExample Ingredients (pbw) 1 2 3 4 5 6 7 8 1 2 3 4 Mantle inner layerHimilan 1605 65 Dynaron 6100P 35 Behenic acid 20 Calcium hydroxide 2.4Hytrel 4047 100 100 100 Hytrel 4067 100 100 Hytrel 5557 100 Mantle outerlayer Hytrel 1605 65 65 65 65 65 65 40 40 40 Dynaron 6100P 35 35 35 2535 35 35 Himilan 1706 40 40 40 HSB 1516 20 20 20 Hytrel 5557 100 Surlyn8120 75 Surlyn 7930 60 Surlyn 6320 35 Nucrel 9-1 5 Behenic acid 20 20 2020 20 20 20 Calcium hydroxide 2.4 2.4 2.4 2.3 2.4 2.4 2.4 Cover PandexT8260 100 Pandex T8295 100 100 100 100 100 100 100 100 Crossnate EM30 1515 15 15 15 15 Surlyn 7930 60 Surlyn 6320 35 Nucrel 9-1 5 Titaniumdioxide 2 2 2 2 2 2 2 2 2 2

-   Himilan 1605: A sodium ion-neutralized ethylene/methacrylic acid    copolymer ionomer produced by DuPont-Mitsui Polychemicals Co., Ltd.-   Dynaron 6100P: A block copolymer having crystalline olefin blocks.    Produced by JSR Corporation.-   Hytrel 4047, 4067, 5557: Polyester elastomers produced by    DuPont-Toray Co., Ltd.-   Himilan 1706: A zinc ion-neutralized ethylene/methacrylic acid    copolymer ionomer produced by DuPont-Mitsui Polychemicals Co., Ltd.-   HSB 1561: A block polymer having terminal amino groups. Produced by    JSR Corporation.-   Surlyn 8120, 7930, 6320: Ionomer resins produced by E.I. DuPont de    Nemours and Company.-   Nucrel 9-1: A ternary acid copolymer produced by E.I. DuPont de    Nemours and Company.-   Pandex T8260, T8295: Thermoplastic polyurethane elastomers produced    by DIC Bayer Polymer, Ltd.

Crossnate EM30: Produced by Dainichi Seika Colour & Chemicals Mfg. Co.,Ltd. TABLE 3 Example Comparative Example 1 2 3 4 5 6 7 8 1 2 3 4 CoreDiameter 35.3 35.3 35.3 35.3 35.3 37.2 37.2 36.4 35.3 35.3 37.2 37.2(mm) Hardness 3.1 3.1 3.5 3.1 3.5 3.3 3.1 4.3 3.1 2.9 3.1 3.0 (mm)Mantle Thickness 1.20 1.20 1.20 1.20 1.20 — — — 1.20 1.20 — — inner (mm)layer Durometer D D40 D47 D55 D40 D56 — — — D40 D47 — — hardness MantleThickness 1.40 1.40 1.40 1.40 1.40 1.65 1.65 1.65 1.40 1.40 1.65 1.65outer (mm) layer Durometer D D56 D56 D56 D52 D55 D56 D56 D56 D56 D56 D53D57 hardness Cover Thickness 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.5 1.1 1.1 1.11.1 (mm) Durometer D D53 D53 D53 D50 D53 D50 D53 D53 D53 D53 D58 D53hardness Ball Diameter 42.7 42.7 42.7 42.7 42.7 42.7 42.7 42.7 42.7 42.742.7 42.7 (mm) Weight 45.3 45.3 45.3 45.3 45.3 45.3 45.3 45.3 45.3 45.345.3 45.3 (g) Hardness 2.7 2.6 2.8 2.9 3.0 2.8 2.6 3.3 2.7 2.4 2.4 2.4(mm) Flight Initial 68.1 68.1 67.8 67.6 67.6 68.2 68.2 67.4 67.4 67.667.7 67.6 velocity(m/s) Driver Spin (rpm) 2900 3000 2900 2972 3070 28702712 2780 2980 3200 3050 3120 HS 45 Carry (m) 218.2 217.3 218.8 217.4216.3 221.9 223.1 216.6 214.2 215.3 218.3 217.1 (23° C.) Total 242.1240.5 242.5 241.2 238.5 242.6 244.1 238.1 237.5 237.8 240.2 239.5distance(m) Spin on approach 6831 6886 6679 6841 6790 6731 6830 66306816 6793 5980 6540 shot (rpm) Feel Driver soft soft soft soft soft softsoft soft soft hard hard hard Putter soft soft soft soft soft soft softsoft soft hard hard hard Scuff resistance good good good good good goodgood good NG NG NG NG

Japanese Patent Application No. 2002-349726 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A multi-piece solid golf ball comprising a solid core, a mantle of atleast one layer and a cover, wherein the core is obtained by molding andvulcanizing a rubber composition comprising (A) 100 parts by weight of abase rubber which includes 60 to 100 wt % of a polybutadiene of at least60 wt % cis-1,4 structure and synthesized using a rare-earth catalyst,(B) an unsaturated carboxylic acid or an unsaturated carboxylic acidmetal salt or both, (C) one or more organic sulfur compounds selectedfrom the group consisting of thiophenols, thionaphthols halogenatedthiophenols and metal salts thereof, (D) an inorganic filler and (E) 0.1to 0.8 parts by weight of organic peroxide, has a diameter of 30 to 40mm and has a deflection when subjected to a load of 980 N (100 kg) of2.5 to 6.0 mm; the mantle is made primarily of a thermoplastic resin,has a thickness of at least 0.5 mm, has a Durometer D hardness of 30 to70, and includes an outermost layer which is in contact with the coverand has a specific Durometer D hardness; the cover is made primarily ofa thermoplastic polyurethane, has a thickness of 0.5 to 2.5 mm and has aDurometer D hardness of 40 to 60 which is lower than the Durometer Dhardness of the outermost layer of the mantle; and the golf ball has adeflection when subjected to a load of 980 N (100 kg) of 2.0 to 4.0 mm.2. The golf ball of claim 1, wherein the outermost layer of the mantlein contact with the cover has a Durometer D hardness of 45 to
 70. 3. Thegolf ball of claim 1, wherein the polybutadiene in the base rubber ofthe rubber composition is a modified polybutadiene rubber synthesizedusing a neodymium catalyst, followed by reaction with a terminalmodifier.
 4. (canceled).
 5. (canceled).
 6. (canceled).
 7. (canceled). 8.The golf ball of claim 1, wherein at least one layer of the mantle ismade primarily of a thermoplastic polyester.
 9. A four-piece solid golfball comprising a solid core, a two-layer mantle and a cover, whereinthe core is obtained by molding a vulcanizing a rubber compositioncomprising (A) 100 parts by weight of a base rubber which includes 60 to100 wt % of a polybutadiene of at least 60 wt % cis-1,4 structure andsynthesized using a rare-earth catalyst, (B) an unsaturated carboxylicacid or an unsaturated carboxylic acid metal salt or both, (C) one ormore organic sulfur compounds selected from the group consisting ofthiophenols, thionaphthols, halogenated thiophenols, and metal saltsthereof, (D) an inorganic filler and (E) 0.1 to 0.8 part by weight oforganic peroxide, has a diameter of 30 to 40 mm and has a deflectionwhen subjected to a load of 980 N (100 kg) of 2.5 to 6.0 mm; the mantleis composed of an inner layer and an outer layer which is in contactwith the cover, each of the two layers being made of a thermoplasticresin, having a thickness of 0.5 to 2 mm and having a Durometer Dhardness of 30 to 70; the cover is made primarily of a thermoplasticpolyurethane, has a thickness of 0.5 to 2.5 mm and has a Durometer Dhardness of 40 to 60 which is lower than the Durometer D hardness of theouter layer of the mantle; and the golf ball has a deflection whensubjected to a load of 980 N (100 kg) of 2.0 to 4.0 mm.
 10. The golfball of claim 9, wherein the outer layer of the mantle in contact withthe cover has a Durometer D hardness of 45 to
 70. 11. The golf ball ofclaim 9, wherein the polybutadiene in the base rubber of the rubbercomposition is a modified polybutadiene rubber synthesized using aneodymium catalyst, followed by reaction with a terminal modifier. 12.(canceled).
 13. (canceled).
 14. (canceled).
 15. (canceled).
 16. The golfball of claim 9, wherein the outer layer of the mantle is made primarilyof a thermoplastic polyester.
 17. The golf ball of claim 9, wherein theinner layer of the mantle is made primarily of a thermoplasticpolyester.
 18. A multi-piece solid golf ball comprising a solid core, amantle of at least one layer and a cover, wherein the core is obtainedby molding and vulcanizing a rubber composition comprising (A) 100 partsby weight of a base rubber which includes 60 to 100 wt % of apolybutadiene of at least 60 wt % cis-1,4 structure and synthesizedusing a rare-earth catalyst, (B) an unsaturated carboxylic acid or anunsaturated carboxylic acid metal salt or both, (C) an organic sulfurcompound, (D) an inorganic filler and (E) 0.1 to 0.8 parts by weight oforganic peroxide, has a diameter of 30 to 40 mm and has a deflectionwhen subjected to a load of 980 N (100 kg) of 2.5 to 6.0 mm; the mantleis made primarily of a thermoplastic resin, has a thickness of at least0.5 mm, has a Durometer D hardness of 30 to 70, and includes anoutermost layer which is in contact with the cover and has a specificDurometer D hardness; the cover is made primarily of a thermoplasticpolyurethane, has a thickness of 0.5 to 2.5 mm and has a Durometer Dhardness of 40 to 60 which is lower than the Durometer D hardness of theoutermost layer of the mantle; and the golf ball has a deflection whensubjected to a load of 980 N (100 kg) of 2.0 to 4.0 mm, wherein therubber composition from which the core includes: (A) 100 parts by weightof a base rubber, (B) 10 to 60 parts by weight of an unsaturatedcarboxylic acid or an unsaturated carboxylic acid metal salt or both,(C) 0.1 to 5 parts by weight of an organic sulfur compound, (D) 5 to 80parts by weight of an inorganic filler, and (E) at least two differentorganic peroxides.
 19. A multi-piece solid golf ball comprising a solidcore, a mantle of at least one layer and a cover, wherein the core isobtained by molding and vulcanizing a rubber composition comprising (A)100 parts by weight of a base rubber which includes 60 to 100 wt % of apolybutadiene of at least 60 wt % cis-1,4 structure and synthesizedusing a rare-earth catalyst, (B) an unsaturated carboxylic acid or anunsaturated carboxylic acid metal salt or both, (C) an organic sulfurcompound, (D) an inorganic filler and (E) 0.1 to 0.8 parts by weight oforganic peroxide, has a diameter of 30 to 40 mm and has a deflectionwhen subjected to a load of 980 N (100 kg) of 2.5 to 6.0 mm; the mantleis made primarily of a thermoplastic resin, has a thickness of at least0.5 mm, has a Durometer D hardness of 30 to 70, and includes anoutermost layer which is in contact with the cover and has a specificDurometer D hardness; the cover is made of a composition consistingessentially of: (G) a thermoplastic polyurethane material, and (H) anisocyanate mixture obtained by dispersing (h1) an isocyanate compoundbearing as functional groups at least two isocyanate groups per moleculein (h2) a thermoplastic resin which substantially does not react withisocyanate, and has a thickness of 0.5 to 2.5 mm and has a Durometer Dhardness of 40 to 60 which is lower than the Durometer D hardness of theoutermost layer of the mantle; and the golf ball has a deflection whensubjected to a load of 980 N (100 kg) of 2.0 to 4.0 mm.
 20. Amulti-piece solid golf ball comprising a solid core, a mantle of atleast one layer and a cover, wherein the core is obtained by molding andvulcanizing a rubber composition comprising (A) 100 parts by weight of abase rubber which includes 60 to 100 wt % of a polybutadiene of at least60 wt % cis-1,4 structure and synthesized using a rare-earth catalyst,(B) an unsaturated carboxylic acid or an unsaturated carboxylic acidmetal salt or both, (C) an organic sulfur, (D) an inorganic filler and(E) 0.1 to 0.8 parts by weight of organic peroxide, has a diameter of 30to 40 mm and has a deflection when subjected to a load of 980 N (100 kg)of 2.5 to 6.0 mm; the mantle is made primarily of a thermoplastic resin,has a thickness of at least 0.5 mm, has a Durometer D hardness of 30 to70, and includes an outermost layer which is in contact with the coverand has a specific Durometer D hardness; the cover is made primarily ofa thermoplastic polyurethane, has a thickness of 0.5 to 2.5 mm and has aDurometer D hardness of 40 to 60 which is lower than the Durometer Dhardness of the outermost layer of the mantle; and the golf ball has adeflection when subjected to a load of 980 N (100 kg) of 2.0 to 4.0 mm,wherein at least one layer of the mantle is made of a mixturecomprising: 100 parts by weight of resin components which include a baseresin of (M) an olefin/unsaturated carboxylic acid binary randomcopolymer or a metal ion neutralization product of an olefin/unsaturatedcarboxylic acid binary random copolymer or both, and (N) anolefin/unsaturated carboxylic acid/unsaturated carboxylic acid esterternary random copolymer or a metal ion neutralization product of anolefin/unsaturated carboxylic acid/unsaturated carboxylic acid esterternary random copolymer or both in a weight ratio M/N of 100:0 to25:75, in combination with (P) a non-ionomeric thermoplastic elastomerin a weight ratio (M+N)/P of 100:0 to 50:50; (Q) 5 to 80 parts by weightof a fatty acid or fatty acid derivative having a molecular weight of280 to 1,500, or both; and (R) 0.1 to 10 parts by weight of a basicinorganic metal compound capable of neutralizing un-neutralized acidgroups in the base resin and component Q.
 21. A multi-piece solid golfball comprising a solid core, a mantle of at least one layer and acover, wherein the core is obtained by molding and vulcanizing a rubbercomposition comprising (A) 100 parts by weight of a base rubber whichincludes 60 to 100 wt % of a polybutadiene of at least 60 wt % cis-1,4structure and synthesized using a rare-earth catalyst, (B) anunsaturated carboxylic acid or an unsaturated carboxylic acid metal saltor both, (C) an organic sulfur compound, (D) an inorganic filler and (E)0.1 to 0.8 parts by weight of organic peroxide, has a diameter of 30 to40 mm and has a deflection when subjected to a load of 980 N (100 kg) of2.5 to 6.0 mm; the mantle is made primarily of a thermoplastic resin,has a thickness of at least 0.5 mm, has a Durometer D hardness of 30 to70, and includes an outermost layer which is in contact with the coverand has a specific Durometer D hardness; the cover is made primarily ofa thermoplastic polyurethane, has a thickness of 0.5 to 2.5 mm and has aDurometer D hardness of 40 to 60 which is lower than the Durometer Dhardness of the outermost layer of the mantle; and the golf ball has adeflection when subjected to a load of 980 N (100 kg) of 2.0 to 4.0 mm,wherein at least one layer of the mantle is made of a mixturecomprising: resin components which include at least one base resinselected from the group consisting of (M) olefin/unsaturated carboxylicacid binary random copolymers and metal ion neutralization productsthereof and (N) olefin/unsaturated carboxylic acid/unsaturatedcarboxylic acid ester ternary random copolymers and metal ionneutralization products thereof, in combination with (P) a non-ionomericthermoplastic elastomer in a weight ratio (M+N)/P of 100:0 to 50:50; (Q)a fatty acid or fatty acid derivative having a molecular weight of 280to 1,500, or both; (R) a metal ion source capable of neutralizingun-neutralized acid groups in the base resin and component Q; and (S) acompound which has a molecular weight of not more than 20,000 and bearsat least two reactive functional groups.
 22. A four-piece solid golfball comprising a solid core, a two-layer mantle and a cover, whereinthe core is obtained by molding a vulcanizing a rubber compositioncomprising (A) 100 parts by weight of a base rubber which includes 60 to100 wt % of a polybutadiene of at least 60 wt % cis-1,4 structure andsynthesized using a rare-earth catalyst, (B) an unsaturated carboxylicacid or an unsaturated carboxylic acid metal salt or both, (C) anorganic sulfur compound, (D) an inorganic filler and (E) 0.1 to 0.8 partby weight of organic peroxide, has a diameter of 30 to 40 mm and has adeflection when subjected to a load of 980 N (100 kg) of 2.5 to 6.0 mm;the mantle is composed of an inner layer and an outer layer which is incontact with the cover, each of the two layers being made of athermoplastic resin, having a thickness of 0.5 to 2 mm and having aDurometer D hardness of 30 to 70; the cover is made primarily of athermoplastic polyurethane, has a thickness of 0.5 to 2.5 mm and has aDurometer D hardness of 40 to 60 which is lower than the Durometer Dhardness of the outer layer of the mantle; and the golf ball has adeflection when subjected to a load of 980 N (100 kg) of 2.0 to 4.0 mm,wherein the rubber composition from which the core includes: (A) 100parts by weight of a base rubber, (B) 10 to 60 parts by weight of anunsaturated carboxylic acid or an unsaturated carboxylic acid metal saltor both, (C) 0.1 to 5 parts by weight of an organic sulfur compound, (D)5 to 80 parts by weight of an inorganic filler, and (E) at least twodifferent organic peroxides.
 23. A four-piece solid golf ball comprisinga solid core, a two-layer mantle and a cover, wherein the core isobtained by molding a vulcanizing a rubber composition comprising (A)100 parts by weight of a base rubber which includes 60 to 100 wt % of apolybutadiene of at least 60 wt % cis-1,4 structure and synthesizedusing a rare-earth catalyst, (B) an unsaturated carboxylic acid or anunsaturated carboxylic acid metal salt or both, (C) an organic sulfurcompound, (D) an inorganic filler and (E) 0.1 to 0.8 part by weight oforganic peroxide, has a diameter of 30 to 40 mm and has a deflectionwhen subjected to a load of 980 N (100 kg) of 2.5 to 6.0 mm; the mantleis composed of an inner layer and an outer layer which is in contactwith the cover, each of the two layers being made of a thermoplasticresin, having a thickness of 0.5 to 2 mm and having a Durometer Dhardness of 30 to 70; the cover is made of a composition consistingessentially of: (G) a thermoplastic polyurethane material, and (H) anisocyanate mixture obtained by dispersing (h1) an isocyanate compoundbearing as functional groups at least two isocyanate groups per moleculein (h2) a thermoplastic resin which substantially does not react withisocyanate, and has a thickness of 0.5 to 2.5 mm and has a Durometer Dhardness of 40 to 60 which is lower than the Durometer D hardness of theoutermost layer of the mantle; and the golf ball has a deflection whensubjected to a load of 980 N (100 kg) of 2.0 to 4.0 mm.
 24. A four-piecesolid golf ball comprising a solid core, a two-layer mantle and a cover,wherein the core is obtained by molding a vulcanizing a rubbercomposition comprising (A) 100 parts by weight of a base rubber whichincludes 60 to 100 wt % of a polybutadiene of at least 60 wt % cis-1,4structure and synthesized using a rare-earth catalyst, (B) anunsaturated carboxylic acid or an unsaturated carboxylic acid metal saltor both, (C) an organic sulfur compound, (D) an inorganic filler and (E)0.1 to 0.8 part by weight of organic peroxide, has a diameter of 30 to40 mm and has a deflection when subjected to a load of 980 N (100 kg) of2.5 to 6.0 mm; the mantle is composed of an inner layer and an outerlayer which is in contact with the cover, each of the two layers beingmade of a thermoplastic resin, having a thickness of 0.5 to 2 mm andhaving a Durometer D hardness of 30 to 70; the cover is made primarilyof a thermoplastic polyurethane, has a thickness of 0.5 to 2.5 mm andhas a Durometer D hardness of 40 to 60 which is lower than the DurometerD hardness of the outer layer of the mantle; and the golf ball has adeflection when subjected to a load of 980 N (100 kg) of 2.0 to 4.0 mm,wherein at least one layer of the mantle is made of a mixturecomprising: 100 parts by weight of resin components which include a baseresin of (M) an olefin/unsaturated carboxylic acid binary randomcopolymer or a metal ion neutralization product of an olefin/unsaturatedcarboxylic acid binary random copolymer or both, and (N) anolefin/unsaturated carboxylic acid/unsaturated carboxylic acid esterternary random copolymer or a metal ion neutralization product of anolefin/unsaturated carboxylic acid/unsaturated carboxylic acid esterternary random copolymer or both in a weight ratio M/N of 100:0 to25:75, in combination with (P) a non-ionomeric thermoplastic elastomerin a weight ratio (M+N)/P of 100:0 to 50:50; (Q) 5 to 80 parts by weightof a fatty acid or fatty acid derivative having a molecular weight of280 to 1,500, or both; and (R) 0.1 to 10 parts by weight of a basicinorganic metal compound capable of neutralizing un-neutralized acidgroups in the base resin and component Q.
 25. A four-piece solid golfball comprising a solid core, a two-layer mantle and a cover, whereinthe core is obtained by molding a vulcanizing a rubber compositioncomprising (A) 100 parts by weight of a base rubber which includes 60 to100 wt % of a polybutadiene of at least 60 wt % cis-1,4 structure andsynthesized using a rare-earth catalyst, (B) an unsaturated carboxylicacid or an unsaturated carboxylic acid metal salt or both, (C) anorganic sulfur compound, (D) an inorganic filler and (E) 0.1 to 0.8 partby weight of organic peroxide, has a diameter of 30 to 40 mm and has adeflection when subjected to a load of 980 N (100 kg) of 2.5 to 6.0 mm;the mantle is composed of an inner layer and an outer layer which is incontact with the cover, each of the two layers being made of athermoplastic resin, having a thickness of 0.5 to 2 mm and having aDurometer D hardness of 30 to 70; the cover is made primarily of athermoplastic polyurethane, has a thickness of 0.5 to 2.5 mm and has aDurometer D hardness of 40 to 60 which is lower than the Durometer Dhardness of the outer layer of the mantle; and the golf ball has adeflection when subjected to a load of 980 N (100 kg) of 2.0 to 4.0 mm,wherein at least one layer of the mantle is made of a mixturecomprising: resin components which include at least one base resinselected from the group consisting of (M) olefin/unsaturated carboxylicacid binary random copolymers and metal ion neutralization productsthereof and (N) olefin/unsaturated carboxylic acid/unsaturatedcarboxylic acid ester ternary random copolymers and metal ionneutralization products thereof, in combination with (P) a non-ionomericthermoplastic elastomer in a weight ratio (M+N)/P of 100:0 to 50:50; (Q)a fatty acid or fatty acid derivative having a molecular weight of 280to 1,500, or both; (R) a metal ion source capable of neutralizingun-neutralized acid groups in the base resin and component Q; and (S) acompound having a molecular weight of not more than 20,000 which bearsat least two reactive functional groups.